Thanks so much for the login credentials @levonau 
Your problem is caused by an incorrect HTML structure and is exacerbated by a discrepancy between canvas and front end, which we have had a task for a very long time but has not yet been resolved: WIP: Nav nestable: elements other than text link or dropdown aren't wrapped with li's on the canvas - #2 by timmse
Please have a look at this screen recording for more details:
I fixed your top level structure, but you should definitely take care of your mega menu as well 